Valve control mechanism

ABSTRACT

An internal combustion engine is disclosed. The engine includes a camshaft carrying a plurality of cams, the camshaft being mounted in a cylinder head or cam carrier; and a valve control mechanism comprising: (a) first means for effecting a limited degree of axial movement of the camshaft; and (b) second means for varying the rotational phase of said camshaft, characterised in that said first and second means comprise a pair of concentric pistons housed within a cylinder and under independent hydraulic control, whereby the concentric pistons can be moved independently of one another. This arrangement enables the valve lift, duration and timing to be varied when the camshaft carries 3-D profiled cam lobes (i.e. valve lift varies tangentially with cam angle in end view and varies along the camshaft linearly at each cam angle in side view).

BACKGROUND

[0001] This invention relates to a valve control mechanism for an internal combustion engine, to engines containing such mechanisms and to a method of operating the valves of an internal combustion engine.

OUR PRIOR PATENT AND PATENT APPLICATIONS

[0002] Our British Patent No. 2 190 140B describes and claims a valve control mechanism which comprises: a camshaft carrying a plurality of cams, the camshaft being mounted in a cam carrier and being arranged for a limited degree of axial movement and having associated with it means for effecting such movement, each of the cam surfaces having an outline, in a section plane containing the axis of the camshaft, which is not parallel to that axis, whereby in use the valve action is a function of the axial location of the camshaft within the range of permitted axial movement, the mechanism also comprising a cam follower for each cam, the cam follower comprising a one-piece body which reciprocates within a slideway and at one extremity acts upon the end of a valve stem through only a shim and has at the opposite extremity a trough of part-circular cross-section which receives a member in the form of a segment of a circular cylinder, the curved surface of which faces the interior surface of the trough, so that said member can turn with respect to said body, whilst a planar side surface of the member faces the cam surface. The present invention offers developments derived from this earlier valve control mechanism.

[0003] Our British Patent Application No. 9925628.1 (filed 29 Oct. 1999 and to be published as GB 2 341 659A on 22 Mar. 2000), and our International Patent Application No. PCT/GB99/03412 filed 15 Oct. 1999, describe and claim several improvements in a valve control system of the type disclosed in GB 2 190 140B. For example, one embodiment of the said British and International Patent Applications relates to a valve control mechanism which comprises: a camshaft carrying a plurality of cams, the camshaft being mounted in, or being adapted to be mounted in, a cylinder head or cam carrier, the valve control mechanism further including means for relatively advancing and retarding the rotation of the camshaft, said advance/retard means comprising a piston housed and axially displaceable within a cylinder, the axial position of said piston being under hydraulic control, and a mechanical coupling between said piston and the camshaft, said mechanical coupling serving to translate the axial movement of said piston into relative rotational movement of said camshaft.

[0004] As disclosed in these our earlier patent applications, the piston and cylinder may be housed within a camshaft pulley at the front end of the camshaft. In one embodiment, the cylinder is defined, at its front end, by a front plate having an annular flange extending towards the camshaft; and at its rear end by the front face of a housing within which said mechanical coupling is housed.

[0005] Advantageously, the mechanical coupling between the piston and the camshaft comprises a spline mechanism acting between said piston and the front end of said camshaft. Such a spline mechanism may be mounted within a housing, the front end surface of said housing forming the rear wall of said cylinder, as indicated above.

[0006] It will be appreciated that the configuration described is such that axial displacement of said piston causes a corresponding degree of rotational advancement of the camshaft when the axial movement is in one direction and a limited degree of rotational retardation of the camshaft when the axial movement is in the opposite direction.

[0007] Preferably, a first channel is provided to deliver hydraulic fluid to the interior of said cylinder directly behind said front plate, and a second channel is provided to deliver hydraulic fluid to said cylinder directly in front of the housing for said mechanical coupling.

[0008] In certain currently preferred embodiments of this earlier invention, the piston is arranged so that its own axial displacement results additionally in axial displacement of the camshaft.

[0009] These our earlier patent applications also disclose a valve control mechanism in which each cam has associated therewith a cam follower comprising a body which reciprocates within a slideway and at one extremity acts upon the end of a valve stem, the cam follower having at its opposite extremity a trough of curved cross-section which receives a member in the form of a segment having on one side thereof a surface curved correspondingly to that of said trough, and having on the other side thereof a planar surface, whereby the curved surface of the segment enables said member to turn with respect to said body, while the planar surface of the member cooperates with the cam surface.

[0010] As disclosed therein, the cam followers are preferably disposed relative to the valve stems such that the zone of action between the each cam follower and the end of its respective valve stem is located away from the mid-point (measured in a direction parallel to the axis of the camshaft) of a section through the cam follower in a plane which contains the axis of the camshaft and the axis of the valve stem. A particularly preferred arrangement disclosed therein is where said end of the valve stem is partly recessed within the body of the cam follower.

[0011] These our earlier patent applications disclose that the hydraulic control of the piston action is preferably under microprocessor control.

[0012] Another embodiment disclosed in GB9925628.1 and in PCT/GB99/03412 is in the form of a valve control mechanism which comprises: a camshaft carrying a plurality of cams, the camshaft being mounted in a cylinder head or cam carrier and being arranged for a limited degree of axial movement and having associated with it means for effecting such movement, each of the cam surfaces having an outline in section taken through a plane containing the axis of the camshaft which is not parallel to that axis, whereby in use the valve action is a function of the axial location of the camshaft within the range of permitted axial movement; and a cam follower for each cam, the cam follower comprising a body which reciprocates within a slideway and at one extremity acts upon the end of a valve stem, the cam follower having at its opposite extremity a trough of part-circular cross-section which receives a member in the form of a segment of a circular cylinder, the curved surface of which faces the interior surface of the trough, so that said member can turn with respect to said body, while a planar side surface of the member faces the cam surface,

[0013] In this embodiment, the valve control mechanism may further comprise means for relatively advancing and retarding the rotation of the camshaft. The mechanism may be arranged so that control of the axial displacement of the camshaft acts also to control the relative rotational adjustment of the camshaft. This provides good control of valve action and can be implemented relatively easily. In an alternative arrangement, control of the axial displacement of the camshaft acts independently of the relative rotational adjustment of the camshaft. This permits greater freedom to influence valve action, but requires more control functions within or associated with the engine.

THIS INVENTION

[0014] The present invention is concerned with a valve control mechanism of the type permitting independent control of the “axial” camshaft adjustment and of the “rotational” camshaft adjustment. This permits controlled variation or adjustment of valve lift, duration and timing; thus the control mechanism is termed “VVLDT”—an acronym for “variable valve lift/duration/timing”.

[0015] According to one aspect of the present invention, there is provided an internal combustion engine including a camshaft carrying a plurality of cams, the camshaft being mounted in a cylinder head or cam carrier; and a valve control mechanism comprising: (a) first means for effecting a limited degree of axial movement of the camshaft; and (b) second means for varying the rotational phase of said camshaft, characterised in that said first and second means comprise a pair of concentric pistons housed within a cylinder and under independent control, whereby the concentric pistons can be moved independently of one another.

[0016] Advantageously, the outer piston serves to control the advance/retard function (i.e. the rotational phase adjustment of the camshaft); and the inner piston controls the axial adjustment of the camshaft. Separate control of these parameters allows the valve timing to be adjusted independently of the valve lift and duration when the cams are suitably profiled.

[0017] Advantageously, the position of said pistons is controlled hydraulically. High pressure oil is the preferred hydraulic medium.

[0018] Preferably, the camshaft moves axially along a straight spline in a drive chain sprocket sleeve under the action of said inner piston; the piston can be acted upon by high pressure oil on both sides thus effecting the valve lift & duration changes; concentric with the inner piston is an outer piston also acted upon by high pressure oil on both sides which moves the chain sprocket sleeve containing a straight spline on its inner diameter mounted on the camshaft and a helical spline on its outer diameter mounted in the chain sprocket thus effecting a rotation of the camshaft and thereby changing its timing.

[0019] It is thus advantageous for said sprocket sleeve to have a helical spline on its outer surface, the arrangement being such that movement of said outer piston causes the chain sprocket sleeve to move axially along the camshaft, thereby imparting a rotational movement to said camshaft through the action of said helical spline. In this way the rotational phase of the camshaft is adjusted, thus in use altering the valve timing of the engine.

[0020] The primary chain drive system in the present invention may be generally the same as that disclosed in our prior patent applications except for a new sprocket design which is preferably mounted on two angular contact ball bearings mounted on a large diameter bearing housing which is part of the new bearing carrier. These bearings are capable of taking radial, axial & tilting loads.

[0021] The second chain drive behind the forward primary drive sprocket is preferably replaced by repositioned helical gears which are part of the sprocket & located just behind the drive sprocket on the inlet side & via a similar gear with no sprocket on the exhaust side whose mounting is offset rearwards; the camshafts thus contra-rotate.

[0022] Both pistons can be prevented from rotating—e.g. in the case of the inner piston by two radial thrust rollers; and by two angular contact ball bearings in the case of the outer piston.

[0023] Advantageously, the cam lobes are mounted on the camshaft in pairs. In preferred embodiments of the engine of this invention, the cam bearings are re-positioned on either side of the cam lobe pairs instead of between them as in the standard engine shown in our earlier patent applications mentioned above.

[0024] It is possible to package the valve control device in a compact form within an existing cylinder head/cover length and overall width for an existing engine installation in a car.

[0025] The new sprocket mounting and gear arrangement just described makes it possible to provide a drive train which is much stiffer than with conventional valve control mechanisms. Furthermore, the loads associated with this new sprocket mounting and gear arrangement are separated from the VVLDT actuating device; and the internal space in the sprocket below the bearing mounting can be utilized to allow the compact installation of this combined device.

[0026] For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

[0027]FIG. 1 is a sectional view through part of an internal combustion engine in accordance with our earlier patent applications (GB9925628.1 and PCT/GB99/03412), with certain parts omitted for the sake of clarity;

[0028]FIG. 2 shows a sectional view, taken in the plane containing the valve stems, through part of an internal combustion engine in accordance with the present invention, the concentric pistons of the VVLDT device being at one extreme of their permitted movement;

[0029]FIG. 3 shows a sectional view corresponding to that of FIG. 2, but with the concentric pistons at the other extreme of their permitted movement;

[0030]FIG. 4 shows a view from the front end of the engine (i.e. from the right as seen in FIGS. 1 and 2); and

[0031]FIG. 5 shows a horizontal sectional view through the engine of FIGS. 2 and 3.

[0032] Referring to FIGS. 1, 2 and 3 of the drawings, similar components are marked with the same reference numbers. In each of these figures, the valve control mechanism comprises an overhead camshaft 4 which carries a plurality of profiled cams 5. Each of the cams 5 cooperates with a half roller 16 which sits in a recess 19 formed on the upper surface of a rectangular cam follower body 6. The half roller 16 is in the form of a segment of a circular cylinder and is free to rotate about its longitudinal axis while seated in the recess 19. Valve stem 1 cooperates with cam follower body 6 and is held in place by retainers 2 (only the upper retainer is shown in FIG. 1) and compression springs 3.

[0033] The cam profiles are three dimensional, i.e. valve lift varies tangentially with cam angle in end view and varies along the camshaft linearly at each cam angle in side view. If desired, the profile of each cam may be such that a line connecting the points of maximum radial extent of the cam at opposite ends (in the direction of the camshaft axis) thereof is non-parallel to the axis of the camshaft.

[0034] In FIG. 1 (our prior patent applications design), the front end of camshaft 4 is connected to a piston 7 located within a cylinder 9 through the intermediary of a spline 8. The chamber of cylinder 9 is defined by a front plate 10 and by an annular flange 11 integral with plate 10; the rear face 12 of the chamber is part of a housing 13 which contains the spline 8. The inner surface 14 of housing 13 is provided with a screw thread (not shown) which cooperates with spline 8 so that axial movement of the spline relative to the housing 13 causes rotation of the spline.

[0035] Housing 13 acts as a carrier for spline 8 and, through the action of bearing surface 40, constitutes an outer bearing for the front end of camshaft 4 within cylinder head or carrier 41. An inner bearing for the front end of camshaft 4 is provided by the outer diameter of splines and the inner spline track diameter. These two (outer and inner) bearings are supported on camshaft pulley bearings 39 via elements 13 and 11, and camshaft pulley 42. The camshaft pulley bearings 39 can accept radial and axial loads and provide a stiffer than conventional means of mounting the camshaft pulley on a circular ring 43 which forms part of the cylinder head structure together with parts 41 and 44.

[0036] In the arrangement of FIG. 1, axial movement of the piston 7 and spline 8 is caused by the supply of oil under pressure to chamber 9 via inlets 15 and 17; oil is supplied to these inlets from proportional programmable valves, e.g. “Moog” valves (not shown). By controlling the hydraulic pressures at inlets 15 and 17, piston 7 is caused to move axially within chamber 9, thereby moving spline 8 and camshaft 4 by a corresponding axial amount. This movement, in turn, causes an additional rotational movement of spline 8, thereby rotationally advancing or retarding the camshaft within pre-set limits (e.g. as defined by the number and disposition of the helical grooves 20-27 formed in cylinder 18).

[0037] The effect of axial movement of camshaft 4 will be discerned from FIG. 1: movement to the left causes the valve stem 1 to rise relative to its previous position at the same point in its cycle, thus giving greater valve lift and, if desired, a change in camshaft duration. The rotational advancement imparted by spline 8, 18 additionally advances the valve timing. Movement to the right reverses these effects.

[0038] The VVLDT device in the present invention differs from that of FIG. 1 in that the two functions—axial displacement of the camshaft and its relative rotation to provide an advance/retard effect—are independent of one another rather than linked.

[0039] Referring to FIGS. 2-5, the control mechanism comprises a pair of concentric pistons 101 and 102 disposed within a housing 100. FIG. 2 shows a side view of the cylinder head, cam carrier and camshaft 4 which moves axially along a straight spline in a drive chain sprocket sleeve via inner piston 102 acted upon by high pressure oil on both sides thus effecting the valve lift and duration changes. Concentric with the inner piston is an outer piston 102 also acted upon by high pressure oil on both sides which moves chain sprocket sleeve 105 containing a straight spline 106 on its inner diameter mounted on the camshaft and a helical spline 107 on its outer diameter mounted in chain sprocket 108 thus effecting a rotation of the camshaft and changing its timing. This view shows both pistons fully forward.

[0040]FIG. 3 is the same view as FIG. 2 but with both pistons 101 and 102 fully rearwards.

[0041] The primary chain drive system is as standard except for the new sprocket (108) design which is mounted on two angular contact ball bearings 109 mounted on a large diameter bearing housing 110 which is part of the new bearing carrier—shown above the red split line in both FIGS. 2 and 3. These bearings are capable of taking radial, axial and tilting loads.

[0042] The second chain drive behind the forward primary drive sprocket is replaced by repositioned helical gears which are part of the sprocket and located just behind the drive sprocket on the inlet side and via a similar gear with no sprocket on the exhaust side whose mounting is offset rearwards—see FIG. 5. The camshafts thus contra-rotate.

[0043] Both pistons 101 and 102 are prevented from rotating—in the case of the inner piston 102 this is achieved by two radial thrust rollers; and by two angular contact ball bearings 110 in the case of the outer piston.

[0044] In addition:

[0045] 1 The re-positioned cam bearings are located on either side of the cam lobe pairs instead of between them as in the engine of FIG. 1;

[0046] 2 The arrangement of FIGS. 2-5 makes it possible to package the VVLDT device in a compact form within an existing cylinder head/cover length and overall width for an existing engine installation in a production car.

[0047] 3 The advantage of the new sprocket mounting and gear arrangement of FIGS. 2-5 is that the drive train is much stiffer than with convention valve control mechanisms. Furthermore its loads are separated from the VVLDT actuating device; and the internal space in the sprocket below the bearing mounting can be utilized to allow the compact installation of this combined device. 

1. An internal combustion engine including a camshaft carrying a plurality of cams, the camshaft being mounted in a cylinder head or cam carrier; and a valve control mechanism comprising: (a) first means for effecting a limited degree of axial movement of the camshaft; and (b) second means for varying the rotational phase of said camshaft, characterised in that said first and second means comprise a pair of concentric pistons housed within a cylinder and under independent control, whereby the concentric pistons can be moved independently of one another.
 2. An engine as claimed in claim 1, wherein the outer piston serves to control the rotational phase of the camshaft; and the inner piston controls the axial adjustment of the camshaft.
 3. An engine as claimed in claim 1 or 2, wherein the camshaft moves axially along a straight spline in a drive chain sprocket sleeve under the action of said inner piston.
 4. An engine as claimed in claim 3, wherein said sprocket sleeve has a helical spline on its outer surface, the arrangement being such that movement of said outer piston causes the chain sprocket sleeve to move axially along the camshaft, thereby imparting a rotational movement to said camshaft through the action of said helical spline.
 5. An engine as claimed in any preceding claim, wherein the position of said pistons is controlled hydraulically.
 6. An engine as claimed in claim 5, wherein high pressure oil is used as the hydraulic medium.
 7. An engine as claimed in any preceding claim, wherein the cam lobes are mounted on the camshaft in pairs.
 8. An engine as claimed in claim 7, wherein the cam bearings are positioned on either side of the cam lobe pairs. 